1. Field of the Invention
The invention relates to a power receiving device, a power transmitting device and a power transfer system.
2. Description of Related Art
With consideration for a natural environment, an electromotive vehicle, such as a hybrid vehicle and an electric vehicle, has become a focus of attention. The electromotive vehicle drives drive wheels by using electric power of a battery, or the like. In recent years, wireless charging that allows a battery of an electromotive vehicle to be charged contactlessly without using a plug, or the like, has become a focus of attention.
Japanese Patent Application Publication No. 2012-170195 (JP 2012-170195 A) describes the invention that relates to a contactless power supply system. In this contactless power supply system, when the specifications of supplied electric power are different between a power transmitting coil and a power receiving coil, a smaller one of the supplied electric powers is supplied. When the specifications of the gap length are different between the power transmitting coil and the power receiving coil, electric power is supplied in the gap length according to the specifications of the power transmitting coil. JP 2012-170195 A describes that, with the contactless power supply system, it is possible to share the power transmitting coil and the power receiving coil among contactless power supply transformers having different types of specifications.
Japanese Patent Application Publication No. 2011-142559 (JP 2011-142559 A) describes an invention that relates to a power supply system. The power supply system includes a power generating unit, a power supply element, a resonant element and a variable matching unit. The power supply element is formed of a coil that is supplied with electric power generated by the power generating unit. The resonant element is coupled to the power supply element through electromagnetic induction. The variable matching unit has an impedance matching function for electric power at a power supply point of the power supply element. The power supply element is configured to be able to change its diameter. The variable matching unit changes the diameter of the power supply element. JP 2011-142559 A describes that, with the power supply system, it is possible to achieve variable impedance matching at a low loss.